ON THE MAGNETISM OF SOME ORDERED AND DISORDERED RH2+X SYSTEMS

New results of electric and magnetic measurements on several heavy rare-earth dihydrides in the fcc beta-phase are presented (R = Gd, Tb, Dy, Ho). The general observation of several magnetic ordering transitions, even in the pure dihydrides (x = 0) but especially emphasized in the superstoichiometric systems (x > 0), is due to the presence of (sometimes overlapping) incommensurate and commensurate magnetic phases. These are strongly influenced by the ordering state of the x-hydrogen sublattice on the octahedral sites as shown by a quenching treatment across its ordering temperature in the range of 200 - 300 K. The interaction between magnetism and the state of the excess hydrogen atoms x is attributed to modifications of the crystal field level scheme and/or to that of the Fermi surface. Finally, the systems exhibit a tendency towards a metal-insulator transition when approaching the beta-phase limit, x(max)beta.